1. Field of the Invention
The present invention relates in general to methods for inspecting for defects in the shape of such objects as chips, leads, and other constituent components employed in the processes for manufacturing semiconductors, and more particularly, to a method for inspecting defects in the shape of an object by comparing an image of an object to be inspected with a reference image of a reference model in terms of brightness.
2. Description of the Related Art
Conventionally, to inspect defects in the shape of objects such as chips and leads, and other constituent elements used in the production processes of semiconductors, a two-step inspection method has been widely used. The two steps are measurement and comparison.
According to the conventional method, a shape-defect inspection of the object has been carried out by an algorithm to inspect defects in the shape of the object through the two steps of measurement and comparison. Specifically, the conventional method is conducted as follows. First, an object to be inspected is physically measured to build data on the shape thereof, using a brightness distribution of an image. For example, a dimension of an external appearance of the object is physically measured in a linear dimension along a certain direction. Then, the measured data and the reference data of a reference model are compared with each other. As a result of the comparison, if the measured data is within a certain range, which is an allowable error for the reference data, the object is determined to be non-defective in shape. If not, the object is determined to be defective in shape.
References such as Park, U.S. Pat. No. 6,184,976 for APPARATUS AND METHOD FOR MEASURING AN AERIAL IMAGE USING TRANSMITTED LIGHT AND REFLECTED LIGHT, have endeavored to provide an aerial image measuring process to inspect various defects existing on patterns formed on a photo masks, while other references such as Pierrat et al., U.S. Pat. No. 6,091,845 for INSPECTION TECHNIQUE OF PHOTO MASK, contemplates providing an extended defect detection capability able to anticipate defects that would not otherwise be found until after the resist pattern is formed by using different mask elevations and interpolating the edges between masked and unmasked areas.
Shishido et al., U.S. Pat. No. 6,087,673 entitled METHOD OF INSPECTING PATTERN AND APPARATUS THEREOF, relies upon a determination of polarity of the difference image obtained from the comparison of specific pattern edges of two images. An allowable value for variation in the gradation value (that is, the value of light and shade) is either added or subtracted, so that the difference between the gradation values of the two images exerts no influence on the polarity of the difference image.
The conventional method using these steps of measurement and comparison is precise even with units of subpixel. These steps must be repeated however, for all elements representing the morphologic characteristics of the object to be inspected, thereby requiring a large amount of time in measurement and comparison.
To reduce the time of inspection, frequently some elements of the workpiece are only partially measured and compared. Selection of those elements to be precisely measured, and thus the integrity of the inspection and the ultimate determination of whether the object is defective in is shape or not is largely dependent upon the experience of skilled persons.